Of course there were headbutts! Basically, X failed to launch: The
Fedora progress screen just hanged after it appeared everything was
done. According to the detailed boot log (type escape during the
Fedora boot), the last daemon to launch was Avahi, but it launched
[ok]. There was no message that X was trying to start, which I think
is a bug. Since I suspected a graphics-card driver/settings problem,
I changed the runlevel from 5 to 3 in /etc/inittab and then I could
boot up to a login prompt with no problems. Oddly, my USB disk drive
did not mount correctly into /media/name at runlevel 3, and I thought
for a good while that it had been wiped out during the upgrade by some
bug. (After all, the preupgrade instructions only say disks will
``not necessarily'' be wiped out during the install.
)
Fortunately, however, the automount works great at runlevel 5 (GUI
mode), and the files are all there after all.

I had at least two problems that I know about so far:

/etc/X11/xorg.conf needed to be hidden away (there was
something fatal in mine, and it's not required any more - yay!)

something was wrong in my home directory (which I found out by
creating a new user and su'ing to him/her and doing a startx ok).

I figured out problem (1) by searching for ``Fedora 13 radeon hang''
or the like, because I suspected my oft-recalcitrant graphics card,
and hit upon the ``basic test'' for the radeon driver for Fedora 13
testing. One of the instructions was to make sure xorg.conf
did not exist!

Regarding my home-directory problem (2), when I tried startx
as me, xauth tried to create an infinite number of authority
files until there were no more processes and the world locked up. I
tried deleting all .X* and .x* files in my home
directory, but that didn't help. It finally worked to move my home
directory to a new name, copy in a newly created home directory (see
man useradd), and edit all occurrences of the username to my
name (and ownerships, etc.), and delete all cookie-looking
files--this was not too tedious, because the initial user files are
admirably small, but it would have been easier to change my main
username (but of course I refuse to do that--it is not good to let
the computer win, ever). I would submit, by the way, that files
created for a new user should all contain $HOME instead of the actual
username (most do already).

After finally getting logged in as myself under X, I got an SELinux
alert that my home directory was not the right type. This is
surprising because I copied it using cp -rp, where `p' means
``preserve,'' but evidently not all properties were preserved. I was
able to fix that in nautilus (an editable property). I suppose this
could explain the xauth problem, but the error alert said
access was NOT denied due to being in ``permissive'' mode. So, that
lossage is still a mystery, as are the fatal aspects of my old
xorg.conf file.

My HP LaserJet did not work right away, and the error message was that
``There is a missing print filter''.

F13 is looking really good now, but I have some work to do to
carefully move in my prior state. Fortunately, most of my prior state
is a set of links to personal data on a different disk, precisely to
make fresh installs go faster.